Video composition systems are components of consumer electronic devices such as personal computers, media players, video games, and the like. Video composition systems combine data from different sources of visual content for display in a video rendering process. The elements received in the data streams and assembled by a compositor of the video composition system may include still picture/video data and other graphics/user interface (UI) data. For example, a compositor may apply closed captioning or graphical user interface elements such as buttons for playback control, over one or more video streams. The compositor may also perform more complex blending and visual effects between video and UI elements. For example, the video could be blurred before being blended with UI elements.
The various visual elements to be mixed by the compositor may be of different dynamic ranges and color spaces. For example, video may be in a High Dynamic Range (HDR) and/or Wide Color Gamut (WCG) format, while graphics/UI elements may be in a standard dynamic range (SDR) or Standard Color Gamut (SCG) format. The HDR representation of video data may have a transfer function including a definition for a peak brightness. Standard dynamic range (SDR) video, such as sRGB, typically is mapped according to broadcasting service HDTV standards defined by Recommendation ITU-R BT.709-5 (Rec. 709). Rec. 709 defines image format parameters and values for HDTV, including color primaries and white point. Graphics and UI elements are typically designed according to a reference standard dynamic range color space (sRGB) display. Existing video compositing systems mix the video data and graphics/UI in sRGB and display the final frame with limited dynamic range. Typically, UI elements are rendered into the same color space as video.
With the evolution of video coding, capture, and display technologies, the dynamic range of video data may become increasingly divergent from the dynamic range of graphical/UI elements. For example, video data can be of high dynamic range, while the user interface and graphical components remain in standard dynamic range. Alternatively, both video and user interface data may be in high dynamic range, but differ in their ranges. When visual elements to be combined have disparate dynamic ranges and/or color spaces, there are challenges to mixing the visual elements while retaining or mapping color information of the elements and adapting colors and luminance to varying display conditions. Thus, there exists a need for a video compositing system that can combine HDR and/or WCG components with SDR and/or SCG components and/or other HDR and/or WCG components in a cost-effective manner.